Major sources for concern in clinical laboratories are the safety, costs and efficiency of the normal procedures for preparation of specimens, such as blood, prior to analysis. Blood specimens for clinical analyses are commonly collected in evacuated blood collection tubes. Serum or plasma may be isolated from the cellular material by centrifugation and transferred or aliquotted to one or more specialized sample vessels. These sample vessels are used to introduce a portion of the specimen to chemical analyzers.
The hazards, labour and errors associated with these preanalytic accessioning procedures could be reduced by automation.
Several aspects of the aliquotting procedure must receive critical attention:
(1) The process exposes laboratory personnel to the hazard of direct contact with a biological fluid which may contain infectious agents such as hepatitis or acquired immune deficiency syndrome (AIDS). Technology which reduces or prevents the direct contact by permitting automated removal of serum or plasma from the blood collection tube, without need to remove the stopper would considerably reduce the hazard.
(2) Manual handling of glass apparati (syringes, blood collection tubes, pipettes) exposes technologists to hazards of spillage and breakage and may result in the loss of a specimen of high clinical value. Ideally a sample of serum or plasma should be transferred directly from the collection tube to the recipient vessel without the need to manipulate an intermediary transfer device.
(3) There are many different analyzers in common use. These may have unique sampling vessels. Multiple aliquots must often be prepared from one patient blood specimen into a variety of specialized sample vessels for use in different analyzers. A useful technology would be able to use a wide variety of sample vessels. It would respond to an input signal which identified the analysis required. It would then select and position the appropriate vessel to receive the aliquot(s).
(4) It is often necessary to exclude suspended fibrinous or cellular material, e.g., red blood cells, which may interfere with analyses. A desirable feature of technology for dispensing serum or plasma would be a mechanical filter to remove any suspended particulate material.
(5) The volume transferred may have to be accurately metered, both to conserve the specimen and to provide an optimal amount for a particular analyzer. An automated aliquotter should be able to sense the amount of serum or plasma available and dispense controlled volumes into the various aliquot recipient vessels.
(6) Positive identification of the aliquot, e.g., by label, is necessary since a sample is being transferred from one vessel to another and many other specimens of similar appearance may be handled at the same time. A device for automated accessioning should ensure continuity of identity from the source container (blood collection tube) to each of the aliquots. A preferred means of identity would be a label with a unique identifier which is generated or transferred to the recipient vessel.
(7) Any apparatus which is used to convey sample from a source tube to an aliquot vessel should either be used only once or be thoroughly cleaned between uses. Carry over of less than 1 part per million is desirable and ideally ought to be nil.
(8) Further analyses on any individual or group of specimens may be necessary at a later time, consequently any unused sample is often stored for several days. This must be protected from the effects of evaporation and preserved, usually by refrigeration. The ideal device should prevent evaporation and accidental contamination of the specimen but facilitate removal of further aliquots at a later time.
Conventional sample aliquotting is labor-intensive and has not generally been automated to the same degree as other procedures in clinical laboratories. Automation of sample aliquotting could effectively isolate laboratory personnel from the dangers of blood processing while increasing the speed and efficiency of the overall analytical procedure.
For most analyses of centrifuged blood samples it is necessary to dispense a portion of the sample to alternate containers such as analyzer sample cups. This is done in a number of ways.
In the usual procedure a technologist takes a blood collection tube which has been centrifuged and opens it by removing the stopper from the top. This may create aerosols or splash droplets of infectious serum. Many blood collection tubes are made of glass and the force required to remove the stopper occasionally results in a broken tube. Open or broken tubes increase the risk of sample loss and infectious hazard to the technologist.
A simple disposable transfer pipette is often used to transfer a portion of the serum or plasma. Another popular method of dispensing a sample is to decant an aliquot into the additional recipient containers. If this method is used the blood collection tube must also contain a gel or other barrier such as in U.S. Pat. No. 3,852,194 to Zine to prevent cellular material from being decanted with the serum or plasma. This method is even more hazardous than the first because considerable care and skill is required to decant a small volume of serum or plasma and not to spill any.
Some devices have been made which attempt to address these hazards. One such device is the Tip-Top (TM) Dispenser Cap made by Helena Laboratories of Beaumont TX 77704-0752. The Tip Top dispenser is fastened to the open end of a centrifuged blood collection tube, inverted, and then squeezed causing a portion of the sample to be dispensed through an orifice to a sample cup. A disadvantage of the Tip Top dispenser and others like it is that removal of the blood collection tube stopper, a hazardous manual step, is required.
The Pumpette (TM) from Helena Laboratories, Beaumont Tex. 77704-0752 is a disposable, manually operated device which does not require stopper removal to dispense a blood sample from a blood collection tube. However, it delivers only a small stream of serum and its use is slow and cumbersome if large numbers of specimens must be aliquotted quickly.
The CleanTech (TM) system made by CleanTech SCI AG, Langenthal CH-4900, Switzerland consists of several components including a cannula to puncture the stopper, a machine to insert the cannula into the stopper, a pipette to access the sample through the stopper and a pump which fastens to the pipette to draw the sample from the tube. This device goes far to address the hazards of dispensing a sample, but it is a relatively complex device and requires several steps to use.
An important innovation would provide cleaner separation and mechanical filtration of the serum. It is an advantage to detect and avoid aspiration of any fibrous material or to filter it out. Modern analyzers tend to have tiny orifices which are easily clogged by the small clots of fibrin suspended in the serum which may remain or be formed after centrifugation. Some clinical chemistry laboratories filter all serum as a precaution. Filtration may be achieved by a device which is inserted into the open end of the collection tube after centrifugation and permits the one-way flow of serum from the collection tube into a separate sampling container through a filter which prevents fibrin from passing into the serum or plasma sample. Such filtration devices are described, for example, in U.S. Pat. No. 4,464,254 by Dojki and are manufactured and distributed under the name of "serum/plasma filter" by W. Sarstedt, Inc. Other devices have been described by U.S. Pat. No. 3,929,646 by Adler, U.S. Pat. No. 4,602,995 by Cassaday, U.S. Pat. No. 4,487,696 by Ferrara and U.S. Pat. No. 4,142,668 by Lee. However, their use requires additional manipulation of the collection tube, consequent exposure of the user to the blood specimen and risk of contamination of the sample.
A variety of devices have been suggested and used with which sampling is accomplished by means of a cannula inserted through the stopper of a blood collection tube, e.g. Seebaugh WR et al: An automated device for aseptically aspirating serum from blood collection tubes. IEEE Transactions on Biomedical Engineering Vol. BME: 33, No. Jun. 6, 1986, pp 610-616. Such a device may either penetrate the stopper with a large cannula and then insert a smaller one into the serum through the large one (such as on the Paramax (R) Closed Container Sampling (TM) by Baxter, Irvine Calif. 92718; or directly through the stopper as in the Serumax (TM) by Medical Robotics, Inc., Lexington, Ky. 40510. Such systems aspirate part or all of the serum and transfer it to another vessel or directly to the analyzer. A disadvantage of these systems is the need to thoroughly wash all surfaces which contact the serum to reduce analyte carryover from one specimen to another.
Another difficulty with systems which require washing of components which contact the analyte is dilution of the specimen. Systems which require washing generally leave a small residue of water in them after rinsing which then mixes with the next portion of analyte draw into the system. This extra water dilutes the analyte thereby disturbing analytical results.
Some blood collection tubes have been designed to directly incorporate a means to dispense serum, for example U.S. Pat. No. 4,169,060 by Columbus, but these require that all blood specimens be collected in such tubes.
With any cannula which reaches into the serum there is a danger of penetrating or aspirating some of the gel separator material used in some types of blood collection tubes. The Helena Pumpette (TM) has this risk if the operator pushes the fine aspiration tube too far into the tube. The device described by Seebaugh has sensors to detect the gel layer and avoid its penetration by the cannula.
Most systems in the prior art sample from upright tubes and all suffer from the difficulty of monitoring and controlling the depth of sampling. One way to avoid such problems is to sample from closed, inverted tubes. In this way the specimen may be accessed in a way that does not require variable-depth sampling. Some have used this method of sampling, but these systems still have the problems of carryover and dilution.
Aliquots of plasma may be prepared from whole blood with a device such as U.S. Pat. No. 4,847,205 by Burtis. However, the aliquots are very small, being centrifugally distributed into capillaries and the blood must be collected by another apparatus such as a syringe or evacuated blood collection tube and then transferred to this device.
Largely automated aliquotting can be performed with devices such as the Tecan Robotic Sample Processor by Tecan AG, 8634 Hombrechitikon, Switzerland. These devices typically have racks or trays which hold the specimen tube and the vessels for which the aliquots are destined. A sample probe or cannula connected to a pump is manipulated automatically to sip and dispense sample. These devices are generally too inflexible to be of use for the primary aliquotting of samples. They are most suitable for the final dispensing, dilution and sample preparation for a particular analysis, with restricted size and shape of sample and aliquot vessels. Similar robotic systems such as described by U.S. Pat. No. 4,927,545 by Roginski are more flexible in their ability to be adapted to a variety of vessels but require complex programming and use up a great deal of space.
The recipient aliquot containers or sample cups must then be labelled to match the source tube. After one or more aliquots have been dispensed the source tube is usually capped to prevent spillage and evaporation and stored for several days. Occasionally this tube is recovered from storage and more serum or plasma is removed for further testing. The additional cap is an added expense, whereas if the original stopper is used there is increased contact with the hazardous biological fluid.